At first glance, attaching an undermount sink to a granite countertop may seem a difficult project. Holding the sink in place beneath the countertop is a series of clips surrounding the sink perimeter. Epoxy secures these clips in place. While an adhesive-based connection may appear flimsy, the adhesive used is a two-part component epoxy that will hold your sink in place even when filled with water and dishes. Added to this, a seam of caulk further seals the sink against leaks, providing you with trouble-free use that will last you for years.
Use a brush to clear away any dust that was created by cutting the hole for the sink during the countertop manufacturing process. This granite dust can interfere with the adhesive holding the sink in place. Brush along the underside of the countertop to remove the dust, and then wipe it with a clean cloth.
Press the sink in place under the countertop with the edge of the sink surrounding the edge of the cutout in the granite. Have an assistant hold the sink in place, or prop something beneath the sink to hold it steady.
Lay the 2-inch by 4-inch board across the width of the sink atop the granite so that it goes over the sink's drain holes. Place a bar clamp through the drain hole and over the 2-inch by 4-inch board. Use two clamps for a dual-drain sink. Tighten the clamps slightly to hold the sink in place. Adjust the placement of the sink if necessary to make sure it's evenly placed underneath the cut-out hole in the granite. Tighten the clamps a bit more to hold the sink tightly in place.
Place the sink clip along the edge of the sink against the underside of the granite. Mark the location where the hole in the clip meets the countertop with a grease pencil. Mark four clip locations of equal spacing along each edge of the sink. Remove the sink and set it aside.
Drill the mounting holes into the marked spots to the depth of the sink anchors. Clean the holes free of granite dust using the brush and cloth.
Mix the epoxy in a cup and then apply it to the posts of the anchors. Press the posts into the drilled holes. Allow the epoxy to set for 10 minutes.
Place a bead of silicone caulk along the lip of the sink where it will sit against the bottom of the granite countertop. Cover the lip completely around, using a continuous bead of the caulk to make certain there are no breaks that may allow moisture through.
Replace the sink beneath the cut-out hole.
Apply epoxy to the clip where it will sit over the lip of the sink. Place the clip over the rim and across the anchors. Secure the clip in place by mounting a screw through the hole in the clip and into the anchor. Tighten the screw to keep the clip in place, and wait overnight for the epoxy to harden completely before connecting the piping to the sink.
Due to the possibility of fracturing the granite, have a professional cut through the countertop for you if it isn't precut for sink installation.
Wear work gloves and safety goggles throughout the installation process for protection from injury. Wear a face mask when dealing with the adhesive to minimise inhaling the fumes.